The document provides an overview of computer networks and the Internet by introducing key concepts and terminology. It describes the Internet as a network of networks that interconnects millions of computing devices and communication links. Protocols control the sending and receiving of messages and define how network entities communicate. The network is organized into layers with different protocols at each layer, known as the Internet protocol stack.
2. Chapter 1: Introduction
Our goal:
get “feel” and
terminology
more depth, detail
later in course
approach:
use Internet as
example
Overview:
what’s the Internet?
what’s a protocol?
network edge; hosts, access
net, physical media
network core: packet/circuit
switching, Internet structure
performance: loss, delay,
throughput
Protocol layers, service models
History of Internet
3. What’s the Internet: “nuts and bolts” view
PC
Interconnects millions Mobile network
of computing devices:
Global ISP
hosts = end systems
wireless
laptop
running network
cellular
Home network
handheld
apps
Regional ISP
communication links
fiber, copper, radio,
access
points
Institutional network
satellite
wired
links
transmission rate =
bandwidth (bits/sec)
routers: forward
router
packets (chunks of
data)
server
4. What’s the Internet: “nuts and bolts” view
protocols control sending,
receiving of msgs
Global ISP
e.g., TCP, IP, HTTP, Skype
Internet: “network of
networks”
Mobile network
public Internet versus
private intranet
Internet standards
IETF: Internet Engineering
Task Force
RFC: Request For Comments
IETF standard Documents
More than 5000 RFCs
Home network
Regional ISP
Institutional network
5. What’s the Internet: A Service View
infrastructure
that provides services to
applications:
Involve multiple end system
that exchange data with each
other.
Web, VoIP, email, games, ecommerce, file sharing
Applications do not run on the
routers
Communication services provided
to applications:
reliable data delivery from
source to destination
(connection oriented)
“best effort” (unreliable) data
Communication
6. What’s a protocol?
Human Protocols:
“what’s the time?”
“I have a question”
Interview
… specific msgs sent
… specific actions
taken when msgs
received, or other
events
Network Protocols:
machines rather than
humans
all communication
activity in Internet
governed by protocols
protocols define format,
order of msgs sent and
received among network
entities, and actions
taken on msg
transmission, receipt
7. What’s a protocol?
a human protocol and a computer network protocol:
Hi
TCP connection
request
Hi
TCP connection
response
Got the
time?
Get http://www.awl.com/kurose-ross
2:00
<file>
time
8. The Network Edge:
end systems (hosts):
run application programs
e.g. Web, email
at “edge of network”
peer-peer
client/server model
client host requests, receives
service from always-on server
client/server
e.g. Web browser/server;
email client/server
Peer-Peer model:
minimal (or no) use of dedicated
servers
e.g. Skype, BitTorrent, Kazaa
More
in Chapter 2
9. Network Access
Access Networks:
The physical link that connects an end
system to its “edge router”.
Q: How to connect end systems to
edge router?
Access Networks can be loosely classified
into three categories
Residential access networks
Dial up, DSL etc
Institutional access networks (school,
company)
Ethernet
Mobile access networks
Wireless LAN (WiFi)
Wider-area wireless access (WiMAX)
Reading Assignment
10. The Network Core
Mesh of interconnected
routers
the fundamental question: how
is data transferred through
net?
circuit switching:
dedicated circuit per call:
telephone networks
packet-switching: data
sent through network in
discrete “chunks” called
packets
Hotel reservation analogy
11. Network Core: Circuit Switching
End-end resources reserved for the
duration of the call
Three phases
Establish, Transfer,
Disconnect
dedicated resources: no sharing
Guaranteed performance
Very Reliable
Developed for Telephone
networks
Inefficient
Channel capacity dedicated
for duration of connection
If no data, capacity wasted
Set up (connection) takes time
12. Network Core: Packet Switching
Today’s internet is a packet switched network
Each end-end data stream divided into packets
Each packet contains a portion of user data plus some
control info.
Each packet has to find its own route to the destination
No predetermined path
Decision as to which node to hop to in the next step is
taken only when a node is reached.
Resources used as needed
Congestion : packets queue, wait for link use
Reliability
Less reliable
Store and forward switching
Routers receives complete packet before forwarding
Question: What is Cut through Switching?
13. Protocol Layers
Networks are complex!
• many “pieces”:
– hosts
– routers
– links of various
media
– applications
– protocols
– hardware,
software
Question:
Is there any way of
organizing network
architecture?
Answer:
Yes possible with a
layered architecture
14. Organization of air travel
ticket (purchase)
ticket (complain)
baggage (check)
baggage (claim)
gates (load)
gates (unload)
runway takeoff
runway landing
airplane routing
airplane routing
airplane routing
•
A series of steps(actions)
15. Layering of Airline Functionality
ticket (purchase)
ticket (complain)
ticket
baggage (check)
baggage (claim
baggage
gates (load)
gates (unload)
gate
runway (takeoff)
runway (land)
takeoff/landing
airplane routing
airplane routing
airplane routing
departure
airport
airplane routing
airplane routing
intermediate air-traffic
control centers
arrival
airport
Airline functionality can be divided into layers, providing a frame work in
which we can discuss air travel.
• At the ticketing layer and below
– Airline-counter-to-airline-counter transfer of a person.
• At the gate layer
– Departure-gate –to-arrival-gate transfer of a person is accomplished
Layers: each layer implements a service
– via its own internal-layer actions
– Combined with the services directly below it
•
16. Why layering?
Dealing with complex systems:
Discuss a well defined, specific part of a
large and complex system
Modularization eases maintenance, updating
of system
Change of implementation of layer’s
service transparent to rest of system
e.g. change in gate procedure doesn’t
affect rest of system
17. Internet Protocol Stack
To provide structure to design of
network
protocols,
network
designers organize protocols in
layers
Service – says what a layer does
Protocol – says how the service is
implemented
Advantages
Drawbacks
When
taken
together
the
protocols of various layers are
called the Protocol Stack.
Internet Protocol Stack consists
of Five layers
Physical,
Link,
Network,
Transport
and
Application
layers .
Organization of Book
18. Internet Protocol Stack
• Application Layer:
Network applications and their application layer protocols
reside.
Provides user interfaces and support for services such as email, file transfer etc.
Hyper Text Transfer Protocol (HTTP)
File Transfer Protocol (FTP)
Session Initiation Protocol (SIP)
An application layer protocol is distributed over multiple end
systems
The packets of information at the application layer is called
as a message.
19. Internet Protocol Stack
• Transport Layer:
Transports application-layer messages between application
end points.
Transport layer packet is called as a segment
Breaks long messages into shorter segments
There are two Transport Layer Protocols
Transmission Control Protocol (TCP)
Connection Oriented service
Guaranteed delivery of application layer messages
Flow control
Congestion Control
User Datagram Protocol (UDP)
Connectionless service
No reliability, flow control and congestion control